1. Field of the invention
The present invention relates to an integrated circuit for a CD (compact disc) player and, more specifically, relates to processing of subcodes Q being read from a compact disc.
2. Description of the prior art
In a CD system, an 8 bit subcode is added to 32 symbols composed of 24 information symbols (each of which is 8 bits) and 8 parity symbols (each of which is 8 bits). These are EFM (Eight to Fourteen Modulation)-modified and recorded on a disc together with a 24 bit frame synchronization signal of 24 bits as a frame of 588 channel bits. Respective channels P, Q, R, S, T, U, V and W are assigned to subcodes, and the P and Q channels are utilized for finding a cue of a piece of music and for performing a program function 30 that a plurality of pieces of music can be reproduced in accordance with order being programmed in advance. Each channel of the subcodes is composed of 98 frames, that is, 98 bits. Specifically, a format of the subcode Q is constructed by synchronization signals S0, S1 for the subcode of 2 bits, control data of 4 bits, address data of 4 bits, data of 72 bits and CRC (Cyclic Redundancy Code) of 16 bits.
FIG. 2 is an illustrative view showing the data format of the subcode Q. As shown in FIG. 2, the subcode Q includes areas A-I represented by a BCD code of 8 bits other than the control data, the address data, and data of the track number, index, time (seconds, minutes) during a piece of music, the frame number during a piece of music, accumulated or total time (seconds, minutes) and the accumulated or total number of frames assigned to the areas A-I. The subcode Q is normally used for displaying the number and time of the piece of music during reproduction. However in order to find a cue of a piece of music and to perform a program function, the subcode Q which is recorded in a lead-in area formed on an inner periphery of the disc has assigned thereto the data of pieces of music recorded in the disc and data of a lead-out area formed on an outer periphery of the disc.
More specifically, the subcode Q of the lead-in area, as shown in FIG. 3, the area A is "00", area B is assigned the data of the track numbers of the pieces of music recorded in the disc, and areas G and H are assigned the start time of the piece of music of each of the track numbers, and area I is assigned the frame numbers from a start of each of the tracks to a start of each of the pieces of music. Furthermore, indexes called as "A0", "A1" and "A2" exhibit in the area B, and the track number of a first piece of music is recorded in the area G of index "A0" and the track number of a last piece of music is recorded in the area G of index "A1". Start time of the lead-out area is recorded in the areas G and H of index "A2", and the frame numbers to a start of the lead-out area is recorded in the area I of "A2". In addition, in the CD system, the number of the pieces of music capable of being recorded in the disc is 99 at most, that is, N=99. Thus, the kinds of the subcodes Q of the lead-in area become 102 at most.
A circuit for fetching such subcodes Q is normally built-in an integrated circuit for a CD player.
In such a subcode output circuit of a conventional integrated circuit for a CD player, the frame synchronization signal is detected from the EFM signal read from the disc, and the EFM signal following the frame synchronization signal is demodulated so as to obtain a subcode of the 8 bits, and the data of Q-channel in the subcode is applied to a shift register such that the subcodes Q can be stored for each frame to complete data of the subcodes Q. The data of the subcodes Q thus completed is outputted from the shift register to an external circuit, for example, a microcomputer in a bit-serial fashion. The microcomputer uses the subcodes Q being transferred in a bit-serial fashion so as to display the number of the piece of music and the time thereof and to obtain data for movement of an optical pick-up to an object value. A technique similar to the above has been disclosed in detail in, for example, Japanese Patent Laid-open Number 83261/1985.
If and when the above described conventional integrated circuit for a CD player is utilized, in the externally connected microcomputer, in order to perform various functions such as displaying the number of the piece of music, displaying the time or program selection of the piece of music, the subcode Q in the lead-in area must be received and stored in a memory circuit in advance.
However, the number of the subcodes Q in the lead-in area becomes 102 at most as described above, the bit number of the data thereof is 2,448 (=8.times.3.times.102) bits. On the other hand, a capacity of the memory circuit (RAM) of the microcomputer is 1K bits at most and the data necessary for other processing must be stored in the RAM, and therefore, it is impossible to store all of the subcodes Q and thus it is necessary to provide with another RAM to wholly store the subcodes Q. In addition, in the case where the playing time of the piece of music is confirmed by utilizing the subcodes Q in the lead-in area, it is necessary to obtain the time of a start of the piece of music and the time of a start of the next piece of music, and therefore, the RAM which stores the subcodes Q must be accessed twice by the microcomputer and thus a load of a program of the microcomputer becomes large.